Data communication or “Datacom” has traditionally relied on copper wires to transmit data from point to point. For example, a copper communication bus may provide communication between a processor and a data storage medium in a household PC, or between servers in a data center. Communication via a traditional copper communication bus is well understood and benefits from the fact that both the endpoint and communication medium are electrical devices.
Optical communication systems offer the promise of greater bandwidth and speed. However, optical communication systems suffer from the interface required between the optical communication system and electrical devices. In particular, coupling of optical components and electrical components typically results in electrical and optical coupling losses and/or signal distortions. These and other obstacles have been addressed by integrating the optical devices onto the integrated circuits in what is referred to as a Photonic Integrated Circuit (PIC). That is, the optical components/devices are created on semiconductor substrates that allow for integration with traditional semiconductor devices.
The semiconductor material silicon (Si) has been the backbone of integrated circuit technology for many years. However, due to the indirect bandgap of silicon—which complicates the production of light—fabrication of active optoelectronic devices has relied on a different class of semiconductor material referred to herein as III-V type semiconductors. These semiconductor materials include combinations of group III elements Aluminum (Al), Gallium (Ga), Indium (In) with group V elements Nitrogen (N), Phosphorus (P), Arsenic (As), and Antimony (Sb), and include combinations such as Gallium Arsenide (GaAs), Indium Phosphide (InP), Gallium Phosphide (GaP), Gallium Nitride (GaN), and Aluminum Gallium Arsenide (AlGaAs). A characteristic of III-V type semiconductors is the direct band gap, which allows for the fabrication of active optoelectronic devices such as lasers, photodetectors, and light-emitting diodes.
Conventional methods for integrating III-V type semiconductors with traditional silicon integrated circuits have tended to follow two approaches. In the first approach, III-V type semiconductor material is deposited directly on a silicon substrate or processed silicon layer. However, lattice constant differences between silicon and III-V type semiconductor materials results in fatal defects (e.g., dislocations) near the silicon/III-V interface. To overcome these defects, a buffer layer can be deposited between the silicon/III-V interface. However, while progress has been made to decrease the thickness of the buffer layer, thin layers can still represent a source of random, lossy defects that negatively impacts coupling between the active III-V devices and the passive silicon components (e.g., electrical circuits, waveguides, etc.). In the second approach, III-V type semiconductor material is grown on a native III-V type substrate having the same or similar lattice constant and then transferred to a silicon substrate. However, this approach is costly as the cost of producing III-V type semiconductor substrates is far greater than the cost of producing a silicon substrate. In addition, placement of the processed, active III-V device requires precise alignment between the device and the passive component (e.g., waveguide, etc.) to which it is coupled.